The following abbreviations are herewith defined:    3GPP third generation partnership project    ARQ automatic repeat request    CPCH common packet channel    FACH forward access channel    F-DPCH fractional dedicated physical channel    E-DCH enhanced dedicated channel    E-DPCCH enhanced dedicated physical control channel (uplink L1 information concerning data rate)    E-DPDCH enhanced dedicated physical channel (uplink data channels)    E-HICH E-DCH hybrid ARQ indicator channel (in downlink)    E-AGCH E-DCH absolute grant channel (in downlink)    HS high speed    HSUPA high speed uplink packet access    L1 Layer 1 (physical)    Node-B base station    RACH random access channel    TCP transport control protocol    UE user equipment    WCDMA wideband code division multiple access
The data rates for RACH (Release 99) are very low. More specifically, the practical instantaneous data rate is 16 kbps (16 thousand bits per second, or 320 bits in 20 ms) and effectively<10 kbps when preamble power ramping is taken into account. The RACH thus cannot be used in any practical manner for the transmission of large packet calls, and no enhancements to RACH were proposed in later releases (post Release 99). Further, in the event of a failed RACH transmission the retransmission delays can be significant, on the order of seconds.
In addition, in Release 99 the RACH setup times from CELL_FACH to CELL_DCH are substantial. This leads to considerably longer delays than needed for medium size packets. Using the HSUPA physical channel increases the data rates considerably. The data transfer in CELL_FACH with the enhanced data rate can continue, except for a small gap, during the switching to CELL_DCH, and can be expected to enhance the end user experience.
A HS-FACH concept has been introduced in 3GPP Release 7, the first proposal of this concept was in R2-061189, “Further discussion on delay enhancements in Rel7”, Nokia, 8th-12 May 2006. The HS-FACH can provide downlink FACH data rates of hundreds of kbps to greater than 1 Mbps (million bits per second). Enhanced FACH is already agreed as part of 3GPP Release 7. See, for example, TS25.214 http://www.3gpp.org/ftp/Specs/archive/25-series/25.214/25214-750.zip 6A.1.1A UE procedure for receiving HS-DSCH and HS-SCCH in CELL_FACH state 6A.1.1B UE procedure for receiving HS-DSCH and HS-SCCH in the URA_PCH and CELL_PCH states,
and TS25.308; http://www.3gpp.org/ftp/Specs/archive/25_series/25.308/25308-730.zip
    14 HS-DSCH reception in CELL_FACH state (FDD only)    15 HS-DSCH reception in CELL_PCH and URA_PCH states (FDD only).
However, in order to obtain the benefit of the improved downlink FACH capability corresponding improvements would be needed in the uplink RACH capabilities. Especially for TCP-based applications, the end user experience will depend mainly on the uplink data rates if the downlink data rates are significantly increased, since TCP acknowledgements are sent in the reverse link and the overall round trip time determines the overall user experience.
A CPCH was included in 3GPP Release 99 specifications and in some subsequent releases as well. The CPCH was intended to be an extension of RACH. Reference in this regard can be made to: 3GPP TS25.211, V4.6.0 (2002-09),3rd generation Partnership Project; Technical Specification Group Radio Access Network; Physical channels and mapping of transport channels onto physical channels (FDD) (Release 4); 3GPP TS25.212, V4.6.0 (2002-09), 3rd generation Partnership Project; Technical Specification. Group Radio Access Network; Multiplexing and channel coding (FDD) (Release 4); 3GPP TS25.213, V4.4.0 (2003-12), 3rd generation Partnership Project; Technical Specification Group Radio Access Network; Spreading and modulation (FDD); 3GPP TS25.214, V4.6.0 (2003-03), 3rd generation Partnership Project; Technical Specification Group Radio Access Network; Physical layer procedures (FDD) (Release 4); and 3GPP TS25.215, V4.8.0 (2005-03), 3rd generation Partnership Project; Technical Specification Group Radio Access Network; Physical layer-Measurements (FDD) (Release 4).
The CPCH was defined in Section 4.1.2.5 of 3GPP TS25.211 as being an uplink transport channel that is associated with a dedicated channel on the downlink which provides power control and CPCH control commands (e.g., emergency stop) for the uplink CPCH. The CPCH is characterized by having an initial collision risk, and by being transmitted using inner loop power control commands.
However, the CPCH was not implemented and it was removed from 3GPP Release 5 specifications. The CPCH thus did not include L1 enhancements, since these enhancements were included for the uplink only with HSUPA in Release 6. The L1 enhancements include fast L1 retransmission, Hybrid ARQ, and fast capacity allocations.